Erdogan was due to arrive in Germany last week to give support to Turkish-German citizens ahead of Turkey's presidential elections in August, but he postponed his visit after the 13 May mining disaster in which 301 people died.

Suleyman Celik, Chairman of the Union of European Turkish Democrats, said on Wednesday the German press had begun publishing "slanderous" and "groundless" news stories about Turkey a week before Erdogan’s visit to Cologne.

- 'No journalistic principles'

Celik said: "Both we, and Turkey, do not deserve this.

"The German press is trying to discredit the government, but there are millions of people [in Turkey] applauding it."